It is estimated that the prevalence of chronic kidney disease in the United States population is 11% (roughly 19.2 million adult individuals) and increasing. The kidneys are organs which function to extract water and urea, mineral salts, toxins, and other waste products from the blood. Patients having one or both defective kidneys often require artificial “dialysis,” a procedure that simulates the function of the kidneys in cleaning wastes from the blood.
There are currently two forms of dialysis available: hemodialysis and peritoneal dialysis. Hemodialysis is a well-known method of providing renal (kidney) function by using a machine to clean wastes and extra fluids from blood and to re-circulate the cleansed blood back into the patient's body. In hemodialysis procedures, blood is withdrawn from the patient's body through an access to a dialysis machine, also commonly referred to as a kidney (or dialysis) machine. In the dialysis machine, toxins and other waste products diffuse through a semi-permeable membrane into a dialysis fluid closely matching the chemical composition of the blood. The filtered blood (i.e., blood with the waste products removed) is then returned to the patient's body. As can be appreciated, proper access to the patient's blood and transport of the blood to and from the dialysis machine for this extended period of time is critical to hemodialysis.
A hemodialysis access (or vascular access) is a large diameter, fast flowing conduit that is located just beneath the skin surface. The superficially located, large diameter, and fast flow conduit/access is typically stuck three times per week with two needles, wherein one needle removes blood from the patient's body and the second needle returns cleansed blood to the patient's body. The blood goes through the dialysis machine and through a special filter called a dialyzer. A patient can receive hemodialysis treatment through either a catheter, graft, or fistula.
A catheter is a temporary access which consists of a tube placed directly into a large vein. With hemodialysis treatment, a catheter is connected directly to a dialysis machine and does not require the use of needles. The catheter may be a single tube with two separate lumens or two separate tubes.
Approximately 70% to 80% of patients in the United States receive hemodialysis through either a fistula or a graft. A fistula is a permanent access that is created when a vein is connected to an artery, usually in a patient's extremity. By directly connecting the vein to the artery, the vein receives “high” or “arterial-like” flow. This results in enlargement in the diameter of the vein to form a “fistula.”
A graft is also a permanent access that is created by a piece of synthetic material (i.e., DACRON) joined from an artery to a vein. This synthetic material is located superficially under the skin and is of adequate diameter for use as a hemodialysis conduit/access.
Despite advances that have been made in providing vascular access for dialysis, few advances have been seen in needles that have been used to cannulate these accesses. Needles used in dialysis are generally 14-17 gauge needles made of stiff material (i.e., metal), have a single end hole, are 1 to 1.5 inches in length, and may or may not include a safety feature to prevent needle sticks. There are a variety of problems associated with currently available needles. Because surgically-created accesses are often deeply positioned, it can be difficult to introduce a needle of only 1 to 1.5 inches in length to the access. Further, due to their shortness in length, current needles will often “back out” of an access during dialysis procedures, which causes returning blood to flow into subcutaneous tissue rather than into the vascular system as intended.
In addition, current needles are generally tubular in shape. Due to their shape and stiffness, current dialysis needles do not have a means for securing their position in the access and will often slide easily out to interrupt hemodialysis treatments. Further, their shape and stiffness often cause posterior access wall punctures. This may damage the graft, fistula, or extremity that is being used for dialysis.
Further, by using needles with a single end hole, the pressure/sheer stress of returning blood (or delivering dialysate fluid) through the single end hole is great. This may cause disruption in blood cell morphology as well as damage to cells lining the graft or fistula. To compensate for this, dialysis needles often have large diameters. Unfortunately, large needle profiles impede insertion of the needle and closure of the needle site. Moreover, for certain individuals, large needles with single end holes lack the ability to efficiently maintain proper flow of fluid volume for effective dialysis.
A further disadvantage of current dialysis needles is the risk involved to administering personnel with inadvertent needle-stick experiences. A substantial risk is present to the administering personnel as dialysis needles are inserted into and removed from a patient for dialysis. Inserted needles can come into contact with bodily fluids that may contain infectious, microbiological agents. Common dangerous blood-borne pathogens include HIV and hepatitis, which have the capability of infecting an individual through an inadvertent needle stick.
Thus, use of current dialysis needles can cause much pain and expense to both the patient and administrator. For example, hemodialysis patients with a surgically-created vascular access (i.e., graft or fistula) often develop bruises due to misplaced needles (infiltration). The risk of infiltration is frequently related to difficult cannulation, deep position of graft or fistula, and/or needle migration during dialysis. Moreover, should the access be damaged, further surgery may be required to provide a new access for dialysis.
Approaches currently available to remedy the risk of needle sticks include those disclosed by Sorenson et al. (U.S. Patent Application No. 2002/0123723), Tolkoff et al. (U.S. Pat. No. 5,743,891), and Lee et al. (U.S. Pat. No. 5,693,030). These apparatuses provide a means of preventing needle sticks upon insertion and retraction of a needle from a patient. However, inability to control and provide proper fluid flow through a needle that would function for effective dialysis as well as the risk of infection and clotting are still problems associated with the above-referenced safety needles.
Recent advancements in the development of biocompatible shape-memory materials are particularly germane to expanding the ability of current dialysis needle technology to allow for prevention of needle migration and posterior access wall puncture, as well as to provide optimal fluid exchange. Shape-memory polymers and alloys, in particular, have been investigated for certain medical applications, namely stents, sutures, and closing plugs. These polymers or alloys were developed to have one shape at one condition (i.e., low temperature) and another shape at a second condition (i.e., high temperature).
Hence, despite the availability of the above needles and safety needles, there is a continuing need for an improved dialysis needle that prevents potential needle stick experiences while facilitating dialysis, helping to secure the needle during dialysis to prevent needle migration and/or dislodgement, reducing sheer stress of blood flow, and reducing the risk of other complications associated with dialysis procedures.